2 Steps to calculate how long will a 12v battery last with inverter

The table below provides a simplified runtime estimate for a 12V battery under two scenarios: when the inverter is running at full rated load and when it's operating with no load (assuming 5% self-consumption).

Inverter Rated Power	12V Battery Runtime at Full Load	12V Battery Runtime with No Load (5%)
500W	2.4 hours	48 hours
1000W	1.2 hours	24 hours
1500W	0.8 hours	16 hours
2500W	0.48 hours	9.6 hours
3000W	0.4 hours	8 hours

Note:

Most inverters use less than 5% of their rated power when idle. For example, the PowMr 2500W 12V to 220V inverter uses less than 1% when not in use.
These estimates assume the battery is fully charged and completely discharged, without factoring in inverter efficiency or energy losses.

In other words, the runtime of a 12V battery connected to an inverter depends primarily on 4 factors: battery capacity (Ah), battery voltage (V), battey depth of discharge, and the inverter’s power draw (W).

This article will delve into the methods for calculating the duration of battery in the scenario where a load is connected to an inverter, along with the factors that need to be taken into consideration.

For a more precise estimate of how long a 12V battery can run an inverter, let’s outline four key factors that provide a complete answer:

Table of Content

Four factors that affect the run time of a 12v battery with an inverter

2 Steps to calculate how long will a 12v battery last with an inverter

4 Key Factors of 12Volt Battery Duration Time Calculation

Calculating the duration of time that a 12v battery can power an inverter is impossible due to the numerous factors that come into play.

However, in this part, we will explore some of the key factors that influence the average length of time that a 12v battery can sustain an inverter:

4 Key Factors of 12Volt Battery Duration Time

Capacity of the battery
Battery types and depth of discharge
Power consumption
Inverter Efficiency

Factor 1 - How many watts are in a 12volt battery

Watts are a measure of power, while volts are a measure of electric potential or voltage.

The battery capacity, which is measured in ampere-hours (Ah) or milliampere-hours (mAh), is conclusive to figure out the number of watts in a 12-volt battery.

To calculate the power in watts, you need to use the formula P = VI, where P is power in watts, V is the voltage of the battery (in this case, 12 volts), and I is the current output of the battery (measured in amperes or milliamperes). Alternatively, the formula to calculate the number of watts in a battery is:

Watts = Volts x Amps

For example, if you have a 12-volt battery with a capacity of 100 Ah, the number of watts would be:

Watts = 12 volts x 100 amps = 1200 watts

So, a 12-volt battery with a capacity of 100 Ah has 1200 watts of power.

Factor 2 - What is the depth of discharge of the battery

Different types of batteries have different discharge depths and the discharge depth affects the battery life and capacity.

Solar power systems typically prefer lithium batteries or other deep cycle battery chemistries, as they can discharge more energy without significantly affecting battery lifespan, often allowing up to 80% depth of discharge.

Factor 3 - How much is the power consumption of the inverter getting from the battery

To calculate how long a 12V battery will last with an inverter, you need to determine the total power consumption of the inverter and the loads connected to the inverter in watts.

The power consumption of the inverter refers to the amount of DC power drawn from the battery to produce a given amount of AC power.

There are two methods to calculate the total power consumption:

1. Estimating with Inverter Rated Power

This method is relatively simple and suitable for rough energy consumption estimation. In practice, the power of the load may vary, but none of the total load power should exceed the rated power of the inverter. Therefore, it can be equated to the load power for calculation without considering the power of the actual connected appliances.

2. Summing Load Power and Inverter No-Load Consumption

Sum up the power of the loads connected to the inverter and the inverter no-load consumption to calculate the total energy consumption. This method is more detailed and accurate. For each load, you can calculate its energy consumption and then add them up to obtain the overall energy consumption.

However, keep in mind that these calculations are an estimate, and the actual battery life will depend on various factors, such as the age and condition of the battery and the temperature, ect.

Factor 4 - What is the inverter efficiency？

Inverter efficiency measures how well DC power from the battery is converted into usable AC power. Some energy is lost as heat, so higher efficiency means less waste and longer battery runtime. Efficiency varies by inverter quality, design and technology of the inverter.

For example, most of PowMr's solar inverters stand out with exceptional efficiency, with most of them boasting peak rates of over 95%.

Factoring efficiency in power calculations gives a more accurate estimate of energy consumption from the battery, crucial for extending battery life and optimizing energy use.

2 Steps to calculate how long will a 12v battery last with an inverter

Having obtained all the necessary values mentioned above:

Next, we will initiate the computation process.

The running time of a battery connected to an inverter is based on the power capacity of the battery and the overall power consumption of the inverter. The two formulas below will give you an estimate of how long the battery will last before it needs to be recharged or replaced.

Formulas

Available battery capacity for inverter
= Battery Capacity x Battery Voltage x DOD% x Inverter Efficiency

Battery Running Time
= Available Battery Capacity for Inverter / Sum of the loads power + Inverter No-load Consumption
or
= Available Battery Capacity for Inverter / Inverter Rated Power

Step 1. Calculate the Available Battery Capacity for Inverter

To ensure accurate calculations and extend battery lifespan, we will take into account the inverter efficiency and battery discharge depth to estimate battery runtime.

Available Battery Capacity for Inverter = Battery Capacity x 12v x DOD% x Inverter Efficiency

Step2. Calculate the Battery Running Time

Divide the available battery capacity for Inverter by the ovelall power consumed by the inverter to get an estimate of the 12v battery life.

Battery Running Time = Battery Capacity x 12v x DOD% x Inverter Efficiency / Inverter Rated Power

Note:As mentioned earlier, you have the option to either utilize the rated power of the inverter as the total power consumption or aggregate the power of the loads connected to the inverter to calculate the overall energy consumption.

Assuming equivalence between the connected load power and the inverter's rated power, we can determine the minimum operating time of the battery. This helps determine the required battery capacity to maintain energy supply during periods without solar input.

How long will a 12v battery run the inverter with loads

Here, we take a 12v 100Ah battery(DOD of 80%) as example.

Based on the two formulas listed above, we can calculate how long will a 12v battery last with inverters of different wattages and efficiency.

How long will a 12v battery last will an 3000W inverter (94% efficiency)

Battery Running Time = 100Ah x 12v x 80% x 94% / 3000W = 0.3008 hours = 19.048 mins

So, battery running time for a 12V battery with a 3000W inverter (94% efficiency) is about 18mins.

How long will a 12v battery last will an 5000W inverter (95% efficiency)

Battery Running Time = 100Ah x 12v x 80% x 95% / 5000W = 0.1824 hours = 10.944 mins

With a 5000W inverter (95% efficiency), a 12V battery will run for 11 mins.

How long will a 12v battery last will an 2000W inverter (92% efficiency)

Battery Running Time = 100Ah x 12v x 80% x 92% / 2000W = 0.4416 hours = 26.496 mins

When powered by a 2000W inverter (92% efficiency), a 12V battery will last 26.496 mins.

How long will a 12v battery last will an 1000W inverter (92% efficiency)

Battery Running Time = 100Ah x 12v x 80% x 92% / 1000W = 0.8832 hours = 52.992 mins

With a 1000W inverter (92% efficiency), a 12V battery's runtime is 52 mins.

How long will a 12v battery last will an 200W inverter (92% efficiency)

Battery Running Time = 100Ah x 12v x 80% x 92% / 200W = 4.416 hours

Employing a 200W inverter (92% efficiency) results in a 12V battery lasting for 4.416 hours.

How long will a 12v battery last will an 500W inverter (92% efficiency)

Battery Running Time = 100Ah x 12v x 80% x 92% / 500W = 1.7664 hours

When connected to a 500W inverter (92% efficiency), a 12V battery will run for 1.7664 hours.

These are the methods for calculating battery life. Again, these calculations are only estimates, and the actual battery runtime may vary depending on a variety of factors (such as the age of the battery, temperature, and usage patterns).